Many computer devices and data servers include an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating, but when the disk rotates air is swirled by the rotating disk. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes at least one coil, a write pole and one or more return poles. When a current flows through the coil, a resulting magnetic field causes a magnetic flux to flow through the write pole, which results in a magnetic write field emitting from the tip of the write pole. This magnetic field is sufficiently strong that it locally magnetizes a portion of the adjacent magnetic disk, thereby recording a bit of data. The write field, then, travels through a magnetically soft under-layer of the magnetic medium to return to the return pole of the write head.
A magnetoresistive sensor such as a Giant Magnetoresistive (GMR) sensor or a Tunnel Junction Magnetoresisive (TMR) sensor has traditionally been employed to read a magnetic signal from the magnetic media. The magnetoresistive sensor has an electrical resistance that changes in response to an external magnetic field. This change in electrical resistance can be detected by processing circuitry in order to read magnetic data from the adjacent magnetic media.
As the need for increased data density increases, the size of magnetic bits recorded on a media must become ever smaller. This in turn can require smaller magnetic grains. However, as the size of the magnetic bits and the associate size of magnetic grains on the magnetic media shrink, the recorded bits can become magnetically unstable. This can be overcome by constructing a magnetic recording system as a thermally assisted magnetic recording system. Such as system uses a magnetic medium that has a high coercivity at room temperature, but a lower coercivity at elevated temperatures. A heat source such as a laser can be used to locally heat the media immediately prior to recording, which temporarily lowers the coercivity of the media so that data can be written. After the data is written the media cools and the data is magnetically stable.